Process for preparing 6-chlorodibenzo[D,F][1,3,2]dioxaphosphepin

ABSTRACT

The present invention relates to a process for preparing 6-chlorodibenzo[d,f][1,3,2]dioxaphosphepin (I) 
                         
which comprises reacting 2,2′-dihydroxybiphenyl with PCl 3  in the presence of a catalytic amount of an acid salt of a nitrogen base, wherein the reaction is carried out in the absence of external organic solvents.

RELATED APPLICATIONS

This application claims benefit (under 35 USC 119(e)) of U.S.Provisional Application Ser. No. 61/581,650, filed Dec. 30, 2011, whichis incorporated herein by reference in its entirety.

BACKGROUND OF THE INVENTION

The present invention relates to a process for preparing6-chlorodibenzo[d,f][1,3,2]dioxaphosphepin(2,2′-biphenylphosphomonochloridite).

PRIOR ART

Organic diphosphite compounds have found extremely widespread use, forexample as chelating ligands in homogeneous catalysis and also as flameretardants, UV stabilizers, etc. Particular rhodium complexes comprisingchelating diphosphite compounds have been found to be useful ascatalysts for the hydroformylation of olefins, since they firstly have ahigh catalytic activity and secondly lead to predominantly linearaldehydes which are preferred for many applications. Organic diphosphitecompounds are also suitable as ligands for transition metal complexcatalysts for hydrocyanation, hydrogenation, carbonylation,hydroacylation, hydroamidation, hydroesterification, hydrosilylation,hydroboration, alcoholysis, isomerization, allylic alkylation orhydroalkylation.

Such diphosphite compounds, their preparation and their use as ligandsin a hydroformylation process are described, for example, in EP 0 214622 A2, EP 0 285 136 A2, U.S. Pat. Nos. 4,668,651, 4,748,261, 4,769,498,4,885,401, 5,235,113, 5,391,801, 5,663,403, 5,728,861, 6,172,267 and DE103 60 771 A1.

Organic diphosphites of the general formula (4) are usually prepared bya process which comprises the following steps:

-   a) reaction of a compound of the formula (1) (=first aromatic diol)    with phosphorus trichloride to give the phosphochloridite (2)

-   b) reaction of the phosphochloridite (2) with a compound of the    formula (3) (=second aromatic diol) to give the chelating    diphosphite (4)

The groups of the organic diphosphites which are derived from the firstaromatic diol (1) will hereinafter also be referred to as “side wings”.

Phosphochloridites of the formula (2) and especially6-chlorodibenzo[d,f][1,3,2]dioxaphosphepin are thus importantintermediates in the preparation of ligands for many homogeneoustransition metal catalysts. There is therefore a continual need forprocesses which allow preparation of these compounds with very effectiveutilization of the starting materials in very high yields and goodpurity. Owing to the toxicity and corrosivity of PCl₃, there is a needfor processes which make possible a very low excess of the PCl₃ used inthe synthesis in order to keep the streams to be handled in thesynthesis, recycling and disposal as small as possible.

In the preparation of phosphomonochloridites and chelating diphosphites,hydrogen halide is obtained in the condensation reaction of the alcoholsor phenols used with PCl₃ and this has to be removed from the reactionmixture. One possibility is neutralization with a base, with nitrogenbases frequently being used. In this procedure, an at leaststoichiometric amount of base based on the hydrogen halide liberated hasto be used. The base is frequently also used in excess. Catalyticactivity of the hydrohalic acid salts of the nitrogen bases in thecondensation reactions has not hitherto been described.

WO 2003/062171 and WO 2003/062251 describe a process for the removal ofacids from reaction mixtures by means of an auxiliary base which withthe acid forms a salt which is liquid at temperatures at which thedesired product is not significantly decomposed during the removal ofthe liquid salt and the salt of the auxiliary base with the desiredproduct or the solution of the desired product in a suitable solventforms two immiscible liquid phases. In other words, the acid salts ofthe auxiliary base behave like ionic liquids which are essentiallyimmiscible with the actual reaction solvent. Preferred auxiliary basesof this type are 1-methylimidazole, 1-n-butylimidazole, 2-methylpyridineand 2-ethylpyridine. The processes described in WO 2003/062171 and WO2003/062251 are suitable, inter alia, for phosphorylation reactions suchas the above-described synthesis of phosphomonochloridites and thereaction thereof with an aromatic diol to give a chelating diphosphitecompound. According to the teaching of WO 2003/062171 and WO2003/062251, the nitrogen base is used in an at least stoichiometricamount based on hydrogen halide liberated.

CN 101684130A describes a process for preparing chelating phosphites, inwhich the phosphomonochloridite forming the side wings is introduced asa solution in dichloromethane into the reaction and the aromatic diolwhich bridges the two phosphorus atoms is introduced as a solution intriethylamine or a triethylamine/dichloromethane mixture. To prepare thephosphochloridite, the document teaches reacting the aromatic diol withfrom 1 to 10 equivalents of PCl₃ and distilling off excess PCl₃. The useof an acid salt of a nitrogen base as catalyst is not described. In thespecific examples, 2,2′-biphenol is reacted with PCl₃ at 100° C. in theabsence of organic solvent. The reaction thus occurs below the meltingpoint of 2,2′-biphenol, i.e. as a suspension of the diol in a largeexcess of PCl₃ (molar ratio of diol:PCl₃=1:6.1). In addition, thisdocument indicates that when the unpurified phosphochloridite obtainedin this way is used in a solvent other than dichloromethane, e.g.toluene, only turbid suspensions are obtained because of the impuritiespresent. However, the inventors of the present invention were able todemonstrate the contrary for the inventive process described below.

WO 2010/052090 and WO 2010/052091 describe processes for preparing6-chlorodibenzo[d,f][1,3,2]-dioxaphosphepin, in which2,2′-dihydroxybiphenyl is added as a melt or as a suspension in an inertsolvent to an excess of phosphorus trichloride under inert gas whilestirring and the gases formed are discharged from the reaction mixtureand neutralized. This process has the disadvantage that the PCl₃ has tobe used in a large molar excess over the diol. Thus, according to thegeneral teaching of these documents, a from 2- to 25-fold excess isused, while an approximately 12-fold excess is used in the examples.These documents do not teach carrying out the reaction in the presenceof a catalyst.

WO 2008/124468 describes a calixarene-bisphosphite composition for useas ligand in a transition metal complex catalyst. In example 1(a), thepreparation of 2,2′-biphenylphosphomonochloridite is described. Here,3.7 equivalents of PCl₃ are added at room temperature to one equivalentof o,o′-biphenyldiol and the suspension obtained is subsequently heateduntil the evolution of HCl abates and subsequently distilled in a highvacuum, with the desired phosphochloridite being obtained in a 78%yield. A significant disadvantage of this procedure is that the reactionis virtually uncontrollable after mixing the reactants and is thusproblematical from a safety point of view. It is less the thermal safetywhich is a problem, since this reaction is endothermic, but rather therisk that on the production scale the HCl discharging system can fail,for example due to an excessively high reaction rate or blockage, whichcan lead to a pressure buildup with the associated consequences.Furthermore, a greater capital investment is necessary since the HClscrubber has to be made larger in order to cope with sudden largeramounts of HCl per unit time.

WO 2010/042313 describes, inter alia, a process for preparingphosphomonochloridites by reacting PCl₃ with an aromatic diol in aslurry which additionally comprises an organic solvent and less than 5mol %, based on the aromatic diol, of a nitrogen base. Specifically, inexample 1 of this document 2,2′-dihydroxybiphenyl is reacted as asuspension in toluene with PCl₃ in the presence of a catalytic amount ofpyridine at 0° C. It is a critical feature of this process that asubstantial part of the aromatic diol used is insoluble in the organicsolvent. Thus, a large molar excess of PCl₃ over the diol is alwaysavailable for the actual reaction in the organic phase, even though theoverall molar excess of PCl₃ is lower. However, this document alsoindicates that undesirable by-products are formed at an excess of PCl₃which is too low.

WO 2009/120210 and the US patent US 2009/0247790 having the samepriority have a disclosure content comparable to that of WO 2010/042313.They describe a process for preparing phosphomonochloridites, in whichthe reaction of PCl₃ with an aromatic diol is carried out in a solutioncomprising less than 5 mol % of a nitrogen base, based on mol ofaromatic diol, with HCl formed being driven off from the reactionsolution and the reaction being carried out under essential isothermalconditions. For the reaction, PCl₃ is initially charged in a reactionzone and a solution or suspension of the diol in an organic solvent isfed into the reaction zone.

It is an object of the present invention to provide a simple, effectiveand safe process for preparing phosphochloridites. It should make thepreparation of the phosphochloridites with very effective utilization ofthe starting materials in very high yields and good purity possible. Thephosphochloridite compound obtained should preferably have a puritywhich allows it to be used as intermediate for the preparation ofchelating phosphites without complicated intermediate purification.

It has now surprisingly been found that this object is achieved by aprocess for preparing phosphochloridites, which comprises reacting anaromatic diol with PCl₃ in the presence of a catalytic amount of an acidsalt of a nitrogen base and in the absence of external organic solvents.It is also surprising that only very small excesses of PCl₃ arenecessary when the PCl₃ is added to a melt of 2,2′-dihydroxybiphenyl,i.e. under process conditions under which the 2,2′-dihydroxybiphenyl isalways present in a relatively high excess over PCl₃ until shortlybefore the end of the reaction. Furthermore, it is surprising that whenthe PCl₃ is introduced into the gas space above the surface of the meltof 2,2′-dihydroxybiphenyl, virtually no loss of PCl₃ due to vaporizationand entrainment in the offgas stream occurs despite the significantlylower boiling point of PCl₃ compared to the melting point of2,2′-dihydroxybiphenyl.

SUMMARY OF THE INVENTION

The invention provides a process for preparing6-chlorodibenzo-[d,f][1,3,2]dioxaphosphepin (I)

which comprises reacting 2,2′-dihydroxybiphenyl (A1)

with PCl₃ in the presence of a catalytic amount of an acid salt of anitrogen base, wherein the reaction is carried out in the absence ofexternal organic solvents.

DESCRIPTION OF THE INVENTION

For the purposes of the invention, the expression “external organicsolvent” refers to components which act as solvent and are differentfrom the starting materials and catalysts used for preparing thephosphochloridites of the general formula (I) and the reaction productsformed.

The product of the 6-chlorodibenzo[d,f][1,3,2]dioxaphosphepin synthesisis soluble in toluene to give a clear solution (at 40° C. as 90%solution and at 20° C. as 50% solution) and can be used without acomplicated work-up to prepare organic diphosphites. To avoidmisunderstandings, it should be pointed out that the production of atoluene solution of (I) serves merely to provide (I) for subsequentreactions and does not represent a work-up or purification step.

The process of the invention has the following advantages:

-   -   It allows the preparation of        6-chlorodibenzo[d,f][1,3,2]dioxaphosphepin (I) in high yields        and with good selectivities.    -   The chlorodibenzo[d,f][1,3,2]dioxaphosphepin is obtained in high        purity.    -   Compared to the processes known from the prior art, the process        requires a very small excess of PCl₃ for the synthesis of the        phosphochloridite. Owing to the toxicity and the corrosivity of        PCl₃, this is particularly advantageous since the PC₁₋₃ streams        to be handled in the synthesis, recycling and disposal can be        kept small.    -   Since no volatile organic solvents are used, the problem of        combustion of the vapors of these solvents before the HCl formed        in the condensation reaction is separated off by scrubbing with        a base does not arise.    -   The acid salts of nitrogen bases, especially N-methylimidazolium        hydrochloride, which are used as catalyst are suitable for the        reaction of PCl₃ with aromatic diols which have a certain        residual water content (up to about 0.3% by weight, based on the        total weight of the diol used). A lower outlay is therefore        required for drying of the diol and its storage and use under        anhydrous conditions.    -   Both the intermediate (A3) and the undesirable by-product (A4)        are found only in traces of <2% in the end product in the        preparation of the phosphochloridites (I) as a result of        addition of the PCl₃ to the initially charged diol (A1).

According to the invention, the reaction of the diol (A1) with PCl₃ iscarried out in the presence of a catalytic amount of an acid salt of anitrogen base.

The acid salt is preferably derived from a nitrogen base selected fromamong in each case unsubstituted or substituted imidazoles, pyridines,1H-pyrazoles, 1-pyrazolines, 3-pyrazolines, imidazolines, thiazoles,oxazoles, 1,2,4-triazoles and 1,2,3-triazoles.

The acid salt is particularly preferably derived from a nitrogen baseselected from among in each case unsubstituted or substituted imidazolesand pyridines.

Particularly preferred nitrogen bases are 3-chloropyridine,4-dimethylaminopyridine, 2-methylpyridine (α-picoline), 3-methylpyridine(β-picoline), 4-methylpyridine (γ-picoline), 2-ethylpyridine,2-ethyl-6-methylpyridine, quinoline, isoquinoline, 1-methylimidazole,1,2-dimethylimidazole, 1-(n-butyl)imidazole, 1,4,5-trimethylimidazole,1,4-dimethylimidazole, imidazole, 2-methylimidazole,1-butyl-2-methylimidazole, 4-methylimidazole, 1-(n-pentyl)imidazole,1-(n-hexyl)imidazole, 1-(noctyl)imidazole, 1-(2′-aminoethyl)imidazole,2-ethyl-4-methylimidazole, 2-ethylimidazole, 1-(2′-cyanoethyl)imidazoleand benzotriazole.

In particular, the acid salt is derived from a nitrogen base selectedfrom among 1-(C₁-C₄-alkyl)imidazoles, 2-(C₁-C₄-alkyl)pyridines,3-(C₁-C₄-alkyl)pyridines and 4-(C₁-C₄-alkyl)pyridines.

The acid salt is especially derived from a nitrogen base selected fromamong 1-methylimidazole, 1-(n-butyl)imidazole, 2-methylpyridine and2-ethylpyridine.

Acids with which the nitrogen bases can form salts are, for example,hydrogen chloride (HCl), hydrogen bromide (HBr), sulfuric acid (H₂SO₄,to form sulfates or hydrogensulfates), methylsulfuric acid(HO(SO₂)OCH₃), ethylsulfuric acid (HO(SO₂)OC₂H₅), phosphoric acid(H₃PO₄, to form phosphates, hydrogenphosphates or dihydrogenphosphates),p-toluenesulfonic acid, benzenesulfonic acid, benzoic acid,2,4,6-trimethylbenzoic acid, mandelic acid, methanesulfonic acid,ethanesulfonic acid or trifluoromethanesulfonic acid. Preferred acidswith which the nitrogen bases can form salts are, for example, hydrogenchloride, p-toluenesulfonic acid, methanesulfonic acid,2,4,6-trimethylbenzoic acid and trifluoromethanesulfonic acid.Particular preference is given to hydrogen chloride.

Especially, N-methylimidazolium hydrochloride is used as acid salt of anitrogen base in the process of the invention.

The amount of acid salt of the nitrogen base used is preferably from0.01 to 5 mol %, particularly preferably from 0.05 to 2 mol %, inparticular from 0.1 to 1 mol %, based on the molar amount of diol (A1).

In the process of the invention, the reaction of the diol (A1) with PCl₃is carried out essentially without addition of free nitrogen bases. Thepreparation of the phosphochloridites of the general formula (I) is thuscarried out according to the process of the invention not as describedin WO 03/062171 and WO 03/062251. That is to say, in the process of theinvention, the hydrogen chloride liberated in the reaction is notseparated off by means of an auxiliary base which with hydrogen chlorideforms a salt which is liquid at temperatures at which thephosphochloridites of the general formula (I) are not significantlydecomposed and the phosphochloridites of the general formula (I) or asolution thereof in a suitable solvent forms two immiscible liquidphases.

The molar ratio of the gradually added PCl₃ to the amount of diol (A1)used is more than 1:1, preferably at least 1.1:1, in particular at least1.2:1, at the end of the reaction.

The molar ratio of the gradually added PCl₃ to the amount of diol (A1)used is preferably not more than 2.5:1, particularly preferably not morethan 2:1, in particular not more than 1.8:1, especially not more than1.6:1, more especially not more than 1.4:1, at the end of the reaction.

As mentioned above, the process of the invention makes it possible toprepare 6-chlorodibenzo[d,f][1,3,2]dioxaphosphepin (I) using only asmall excess of PCl₃.

The reaction is preferably carried out at a temperature in the rangefrom 20 to 250° C., particularly preferably from 50 to 200° C.

In a specific embodiment of the process of the invention for preparingthe phosphochloridites of the general formula (I), the diol (A1) is usedas a melt for the reaction.

To provide a melt, the diol (A1) is heated to a temperature above themelting point so that it goes over into a liquid state. If the diol (A1)is used as a technical-grade compound comprising impurities which lowerthe melting point, the melting point can also be below that of the purecompound. Pure 2,2′-dihydroxybiphenyl melts at from 108 to 110° C.

In a specific embodiment of the process of the invention, the PCl₃ isadded to a melt of the diol (A1).

The PCl₃ is preferably introduced into the space above the melt of thediol (A1). This can be achieved using a conventional addition devicewhose outlet opening ends above the melt. The PCl₃ can be introduced inthe form of individual droplets or as a jet. The amount fed in can beregulated by means of a conventional metering device, e.g. a valve,metering pump, etc. The reaction can thus be carried out in ameteringcontrolled manner. At least those surfaces which come intocontact with the PCl₃ are made of a corrosion-resistant material such asglass, Teflon, enamels, etc.

The boiling point of PCl₃ (76.1° C. at 1013 mbar) is below the meltingpoint of the diol (A1) (108-110° C.). The reaction is thereforepreferably carried out using one of the following measures:

-   -   addition of the PCl₃ in sufficiently small amounts per time        interval,    -   use of a cooling device, e.g. a reflux condenser, in order to        separate off vaporized PCl₃ as condensate and recirculate it to        the reaction zone.

In general, the reaction is carried out at ambient pressure (1013 mbar),but higher or lower pressures can also be used.

In a specific embodiment, the reaction is carried out in the presence ofa gas which is inert under the reaction conditions. Suitable inert gasesof this type are, for example, nitrogen, argon or helium. In a usefulembodiment, the liquid reaction medium is blanketed with an inert gas.In a further useful embodiment, a stream of inert gas is passed throughthe liquid reaction medium. The stream of inert gas passed through theliquid reaction medium can at the same time serve to strip the reactionmedium in order to remove the HCl formed more effectively. In apreferred embodiment, an offgas stream is taken from the reaction zoneand subjected to scrubbing to remove the HCl comprised therein. Suitablewashing media are water and aqueous alkaline washing media.

If the reaction zone is connected to a cooling device, e.g. a refluxcondenser, in order to avoid PCl₃ losses by vaporization, the offgasstream, optionally together with at least one inert gas, is preferablyalso firstly passed through the cooling device and only then the offgasscrubber.

The reaction is preferably carried out until at least 95% by weight ofthe diol (A1), particularly preferably at least 98% by weight of thediol (A1), has been converted into6-chlorodibenzo[d,f][1,3,2]dioxaphosphepin (I).

If the reaction mixture still comprises unreacted PCl₃ after theconclusion of the reaction, this can be separated off by conventionalmethods, preferably by distillation. To separate off the PCl₃ bydistillation, it is possible to employ one of the following measures:

-   -   increasing the temperature of the reaction mixture,    -   applying a reduced pressure,    -   introducing a stream of inert gas into the reaction mixture,    -   a combination of at least two of these measures.

The phosphochloridites obtained by the process of the invention areparticularly advantageous for preparing organic diphosphites.

The invention further provides a process for preparing organicdiphosphites of the general formula (II)

where

-   R¹, R², R³ and R⁴ are each, independently of one another, hydrogen,    C₁-C₁₂-alkyl, C₁-C₁₂-alkoxy, C₃-C₁₂-cycloalkyl,    C₃-C₁₂-heterocycloalkyl, C₆-C₂₀-aryl, chlorine, bromine, hydroxy,    acyl or alkoxycarbonyl,    -   where two adjacent radicals R¹ to R⁴ together with the carbon        atom of the benzene ring to which they are bound can also form a        fused ring system with a further benzene ring,    -   where C₁-C₁₂-alkyl and C₁-C₁₂-alkoxy can each be unsubstituted        or substituted by one or more identical or different radicals        R^(a) selected from among C₃-C₁₂-cycloalkyl,        C₃-C₁₂-heterocycloalkyl, C₆-C₂₀-aryl, fluorine, chlorine, cyano,        acyl and alkoxycarbonyl,    -   where C₃-C₁₂-cycloalkyl and C₃-C₁₂-heterocycloalkyl can each be        unsubstituted or substituted by one or more identical or        different radicals Rb selected from among C₁-C₁₂-alkyl,        C₁-C₁₂-alkoxy, C₃-C₁₂-cycloalkyl, C₃-C₁₂-heterocycloalkyl,        C₆-C₂₀-aryl, fluorine, chlorine, bromine, cyano, formyl, acyl        and alkoxycarbonyl,    -   where C₆-C₂₀-aryl and can each be unsubstituted or substituted        by one or more identical or different radicals Rc selected from        among C₁-C₁₂-alkyl, C₁-C₁₂-alkoxy, C₃-C₁₂-cycloalkyl,        C₃-C₁₂-heterocycloalkyl, C₆-C₂₀-aryl, fluorine, chlorine,        bromine, cyano, formyl, acyl and alkoxycarbonyl,        which comprises-   a) reacting 2,2′-dihydroxybiphenyl (A1)

-   -   with PCIS in the presence of a catalytic amount of an acid salt        of a nitrogen base and in the absence of an external organic        solvent to give 6-chlorodibenzo[d,f][1,3,2]dioxaphosphepin (I),

-   b) reacting the 6-chlorodibenzo[d,f][1,3,2]dioxaphosphepin (I) with    a diol of the general formula (A2)

to give the organic diphosphite (II).

For the purposes of the invention, halogen is fluorine, chlorine,bromine or iodine, preferably fluorine, chlorine or bromine.

In the following, the expression “C₁-C₁₂-alkyl” comprises straight-chainand branched C₁-C₁₂-alkyl groups. Preference is given to straight-chainor branched C₁-C₈-alkyl groups and very particularly preferablyC₁-C₆-alkyl groups. Examples of C₁-C₁₂-alkyl groups are, in particular,methyl, ethyl, propyl, isopropyl, n-butyl, isobutyl, sec-butyl,tert-butyl, n-pentyl, 2-pentyl, 2-methylbutyl, 3-methylbutyl,1,2-dimethylpropyl, 1,1-dimethylpropyl, 2,2-dimethylpropyl,1-ethylpropyl, n-hexyl, 2-hexyl, 2-methylpentyl, 3-methylpentyl,4-methylpentyl, 1,2-dimethylbutyl, 1,3-dimethylbutyl, 2,3-dimethylbutyl,1,1-dimethylbutyl, 2,2-dimethylbutyl, 3,3-dimethylbutyl,1,1,2-trimethylpropyl, 1,2,2-trimethylpropyl, 1-ethylbutyl,2-ethylbutyl, 1-ethyl-2-methylpropyl, n-heptyl, 2-heptyl, 3-heptyl,2-ethylpentyl, 1-propylbutyl, n-octyl, 2-ethylhexyl, 2-propylheptyl,nonyl, decyl.

The above explanations of the expression “C₁-C₁₂-alkyl” also apply tothe alkyl groups in C₁-C₁₂-alkoxy.

Substituted C₁-C₁₂-alkyl groups and substituted C₁-C₁₂-alkoxy groupscan, depending on their chain length, have one or more (e.g. 1, 2, 3, 4or 5) substituents Ra. The substituents R^(a) are preferably selectedindependently from among C₃-C₁₂-cycloalkyl, C₃-C₁₂-heterocycloalkyl,C₆-C₂₀-aryl, fluorine, chlorine, bromine, cyano, formyl, acyl andalkoxycarbonyl.

For the purposes of the present invention, the expression “alkylene”refers to straight-chain or branched alkanediyl groups having preferablyfrom 1 to 6 carbon atoms.

These include methylene (—CH₂—), ethylene (—CH₂—CH₂—), n-propylene(—CH₂—CH₂—CH₂—), isopropylene (—CH₂—CH(CH₃)—), etc.

For the purposes of the present invention, the expression“C₃-C₁₂-cycloalkyl” comprises monocyclic, bicyclic or tricyclichydrocarbon radicals having from 3 to 12, in particular from 5 to 12,carbon atoms. These include cyclopropyl, cyclobutyl, cyclopentyl,cyclohexyl, cycloheptyl, cyclooctyl, cyclododecyl, cyclopentadecyl,norbornyl, bicyclo[2.2.2]octyl or adamantyl.

For the purposes of the present invention, the expression“C₃-C₁₂-heterocycloalkyl” comprises nonaromatic, saturated or partiallyunsaturated cycloaliphatic groups having from 3 to 12, in particularfrom 5 to 12, carbon atoms. C₃-C₁₂-Heterocycloalkyl groups preferablyhave from 4 to 8, particularly preferably 5 or 6, ring atoms. Incontrast to the cycloalkyl groups, 1, 2, 3 or 4 of the ring carbons inthe heterocycloalkyl groups are replaced by heteroatoms orheteroatom-comprising groups. The heteroatoms or heteroatom-comprisinggroups are preferably selected from among —O—, —S—, —C(═O)— and—S(═O)₂—. Examples of C₃-C₁₂-heterocycloalkyl groups aretetrahydrothiophenyl, tetrahydrofuranyl, tetrahydropyranyl and dioxanyl.

Substituted C₃-C₁₂-cycloalkyl groups and substitutedC₃-C₁₂-heterocycloalkyl groups can, depending on their ring size, haveone or more (e.g. 1, 2, 3, 4 or 5) substituents Rb. The substituents Rbare preferably selected independently from among C₁-C₁₂-alkyl,C₁-C₁₂-alkoxy, C₃-C₁₂-cycloalkyl, C₃-C₁₂-heterocycloalkyl, C₆-C₂₀-aryl,fluorine, chlorine, bromine, cyano, formyl, acyl and alkoxycarbonyl.Substituted C₃-C₁₂-cycloalkyl groups preferably bear one or more, e.g.1, 2, 3, 4 or 5, C₁-C₆-alkyl groups. Substituted C₃-C₁₂-heterocycloalkylgroups preferably bear one or more, e.g. 1, 2, 3, 4 or 5, C₁-C₆-alkylgroups.

Examples of substituted C₃-C₁₂-cycloalkyl groups are 2- and3-methylcyclopentyl, 2- and 3-ethylcyclopentyl, 2-, 3- and4-methylcyclohexyl, 2-, 3- and 4-ethylcyclohexyl, 2-, 3- and4-propylcyclohexyl, 2-, 3- and 4-isopropylcyclohexyl, 2-, 3- and4-butylcyclohexyl, 2-, 3- and 4-sec-butylcyclohexyl, 2-, 3- and4-tert-butylcyclohexyl, 2-, 3- and 4-methylcycloheptyl, 2-, 3- and4-ethylcycloheptyl, 2-, 3- and 4-propylcycloheptyl, 2-, 3- and4-isopropylcycloheptyl, 2-, 3- and 4-butylcycloheptyl, 2-, 3- and4-sec-butylcycloheptyl, 2-, 3- and 4-tert-butylcycloheptyl, 2-, 3-, 4-and 5-methylcyclooctyl, 2-, 3-, 4- and 5-ethylcyclooctyl, 2-, 3-, 4- and5-propylcyclooctyl.

For the purposes of the present invention, the expression “C₆-C₂₀-aryl”comprises monocyclic or polycyclic aromatic hydrocarbon radicals. Thesehave from 6 to 20 ring atoms, in particular from 6 to 14 ring atoms.Aryl is preferably phenyl, naphthyl, indenyl, fluorenyl, anthracenyl,phenanthrenyl, naphthacenyl, chrysenyl, pyrenyl, coronenyl, perylenyl,etc. In particular, aryl is phenyl or naphthyl.

Substituted C₆-C₂₀-aryl groups can, depending on their ring size, haveone or more (e.g. 1, 2, 3, 4 or 5) substituents R^(c). The substituentsR^(c) are preferably selected independently from among C₁-C₁₂-alkyl,C₁-C₁₂-alkoxy, C₃-C₁₂-cycloalkyl, C₃-C₁₂-heterocycloalkyl, C₆-C₂₀-aryl,fluorine, chlorine, bromine, cyano, nitro, formyl, acyl andalkoxycarbonyl.

Substituted C₆-C₂₀-aryl is preferably substituted phenyl or substitutednaphthyl. Substituted C₆-C₂₀-aryl groups preferably bear one or more,e.g. 1, 2, 3, 4 or 5, substituents selected from among C₁-C₆-alkylgroups, C₁-C₆-alkoxy groups, chlorine and bromine.

For the purposes of the present invention, the term “acyl” refers toalkanoyl or aroyl groups which generally have from 2 to 11, preferablyfrom 2 to 8, carbon atoms. They include, for example, acetyl, propanoyl,butanoyl, pentanoyl, hexanoyl, heptanoyl-, 2-ethylhexanoyl,2-propylheptanoyl, pivaloyl, benzoyl or naphthoyl.

For the purposes of the present invention, the term carboxylatepreferably refers to a derivative of a carboxylic acid function, inparticular a carboxylic ester function or a carboxamide function. Suchfunctions include, for example, esters with C₁-C₄-alkanols such asmethanol, ethanol, n-propanol, isopropanol, n-butanol, sec-butanol andtertbutanol. They also include the primary amides and their N-alkyl andN,N-dialkyl derivatives.

Fused ring systems can be aromatic, hydroaromatic and cyclic compoundsjoined by fusion (fused). Fused ring systems comprise two, three or morethan three rings. Depending on the way in which they are joined, adistinction is made among fused ring systems between ortho-fusion, i.e.each ring shares an edge or two atoms with each adjacent ring, andperi-fusion in which a carbon atom belongs to more than two rings. Amongfused ring systems, preference is given to ortho-fused ring systems.

As regards step a), what has been said above for the preparation ofphosphochloridites of the general formula (I) is fully incorporated byreference.

Step b)

In the organic diphosphites of the general formula (II), preference isgiven to the radicals R³ and R⁴ together forming a fused-on benzene ringand R¹ and R² each being hydrogen, i.e. the group of the formula

The diols of the general formula (A2)

are preferably selected from among3,3′,5,5′-tetramethyl-1,1′-biphenyl-2,2′-diol,3,3′,5,5′-tetraethyl-1,1′-biphenyl-2,2′-diol,3,3′,5,5′-tetra-n-propyl-1,1′-biphenyl-2,2′-diol,3,3′-dimethyl-5,5′-dichloro-1,1′-biphenyl-2,2′-diol,3,3′-diethyl-5,5′-dibromo-1,1′-biphenyl-2,2′-diol,3,3′-dimethyl-5,5′-diethyl-1,1′-biphenyl-2,2′-diol,3,3′-dimethyl-5,5′-din-propyl-1,1′-biphenyl-2,2′-diol,3,3′,5,5′-tetraisopropyl-1,1′-biphenyl-2,2′-diol,3,3′,5,5′-tetra-n-butyl-1,1′-biphenyl-2,2′-diol,3,3′,5,5′-tetraisobutyl-1,1′-biphenyl-2,2′-diol,3,3′,5,5′-tetra-sec-butyl-1,1′-biphenyl-2,2′-diol,3,3′,5,5′-tetra(1,1-dimethylethyl)-1,1′-biphenyl-2,2′-diol,3,3′-di(1,1-dimethylethyl)-5,5′-di-n-amyl-1,1′-biphenyl-2,2′-diol,3,3′,5,5′-tetrakis(1,1-dimethylpropyl)-1,1′-biphenyl-2,2′-diol,3,3′-di(1,1-dimethylethyl)-5,5′-bis(1,1-dimethylpropyl)-1,1′-biphenyl-2,2′-diol,3,3′-di(1,1-dimethylethyl)-5,5′-di-nhexyl-1,1′-biphenyl-2,2′-diol,3,3′-di(1,1-dimethylethyl)-5,5′-di-2-hexyl-1,1′-biphenyl-2,2′-diol,3,3′-di(1,1-dimethylethyl)-5,5′-di-3-hexyl-1,1′-biphenyl-2,2″-diol,3,3′-di(1,1-dimethylethyl)-5,5′-di-n-heptyl-1,1′-biphenyl-2,2″-diol,3,3′-di(1,1-dimethylethyl)-5,5′-di-2-heptyl-1,1′-biphenyl-2,2′-diol,3,3′-di(1,1-dimethylethyl)-5,5′-di-3-heptyl-1,1′-biphenyl-2,2′-diol,3,3′-di(1,1-dimethylethyl)-5,5′-di-4-heptyl-1,1′-biphenyl-2,2′-diol,3,3′-di(1,1-dimethylethyl)-5,5′-di-n-octyl-1,1′-biphenyl-2,2′-diol,3,3′-di(1,1-dimethylethyl)-5,5′-di-2-octyl-1,1′-biphenyl-2,2′-diol,5,5′-di-3-octyl-1,1′-biphenyl-2,2′-diol,3,3′-di(1,1-dimethylethyl)-5,5′-di-4-octyl-1,1′-biphenyl-2,2′-diol,3,3′-di(1,1-dimethylethyl)-5,5′-bis(1,1,3,3-tetramethylbutyl)-1,1′-biphenyl-2,2′-diol,3,3′,5,5′-tetrakis(1,1,3,3-tetramethylbutyl)-1,1′-biphenyl-2,2′-diol,3,3′-di(1,1-dimethylethyl)-5,5′,6,6′-tetramethyl-1,1′-biphenyl-2,2′-diol,3,3′-di(1,1-dimethylethyl)-5,5′-diphenyl-1,1′-biphenyl-2,2′-diol,3,3′-di(1,1-dimethylethyl)-5,5′-bis(2,4,6,-trimethylphenyl)-1,1′-biphenyl-2,2′-diol,3,3′-di(1,1-dimethylethyl)-5,5′-dimethoxy-1,1′-biphenyl-2,2′-diol,3,3′-di(1,1-dimethylethyl)-5,5′-diethoxy-1,1′-biphenyl-2,2′-diol,3,3′-di(1,1-dimethylethyl)-5,5′-di-n-propoxy-1,1′-biphenyl-2,2′-diol,3,3′-di(1,1-dimethylethyl)-5,5′-di-isopropoxy-1,1′-biphenyl-2,2′-diol,3,3′-di(1,1-dimethylethyl)-5,5′-di-n-butoxy-1,1′-biphenyl-2,2′-diol,3,3′-di(1,1-dimethylethyl)-5,5′-di-sec-butoxy-1,1′-biphenyl-2,2′-diol,3,3′-di(1,1-dimethylethyl)-5,5′-diisobutoxy-1,1′-biphenyl-2,2′-diol,3,3′-di(1,1-dimethylethyl)-5,5′-ditert-butoxy-1,1-biphenyl-2,2′-diol and1,1′-binaphthalinyl-2,2′-diol.

The diol (A2) is particularly preferably3,3′,5,5′-tetra(1,1-dimethylethyl)-1,1′-biphenyl-2,2′-diol. That is tosay, particular preference is given to the radicals R¹ and R³ in theorganic diphosphites of the general formula (I) all being tert-butyl andR² and R⁴ all being hydrogen.

The 6-chlorodibenzo[d,f][1,3,2]dioxaphosphepin (I) prepared by theprocess of the invention is particularly useful for preparing thefollowing organic diphosphites (II):

In particular, the organic diphosphite of the formula (II) is6,6′-[[3,3′,5,5′-tetrakis(1,1-dimethylethyl)-1,1′-biphenyl]-2,2′-diyl]bis(oxy)]bisdibenzo[d,f][1,3,2]-dioxaphosphepin.

Step b) of the preparation of the diphosphites (II) can in principle becarried out by means of known phosphorus halide-alcohol condensationreactions, as described, for example, in EP 0 214 622 A2, U.S. Pat. Nos.4,668,651, 4,748,261, 4,769,498, 4,885,401, 5,235,113, 5,391,801,5,663,403, 5,728,861, 6,172,267, WO 2003/062171 and WO 2003/062251.

The reaction in step b) is preferably carried out in the presence of abase.

Suitable bases are generally, for example, alkali metal hydroxides,alkaline earth metal hydroxides, NO₃, alkali metal carbonates, alkalineearth metal carbonates, alkali metal hydrogencarbonates, alkaline earthmetal hydrogencarbonates, tertiary amines and basic ion-exchange resins,etc. These include, for example, NaOH, KOH, Ca(OH)₂, triethylamine,tripropylamine, tributylamine, etc. Preference is given to tertiaryamines and more particularly triethylamine.

In a specific embodiment, the reaction in step b) is carried out bymeans of a process as described in WO 2003/062171 and WO 2003/062251.Here, step b) is then carried out in the presence of a base selectedfrom among bases which with the hydrohalic acid formed in the respectivereaction step form a salt which is liquid at temperatures at which thereaction product of the respective reaction step is not significantlydecomposed during the removal of the liquid salt and the salt forms twoimmiscible liquid phases with the reaction medium of the respectivereaction step.

Suitable bases of this type are described in WO 2003/062171 and WO2003/062251, which are hereby fully incorporated by reference.Preference is given to using a base selected from among1-methylimidazole, 1-n-butylimidazole, 2-methylpyridine and2-ethylpyridine in step b).

In the last-named process variant, the major part of the acid saltsformed from HCl and base in the condensation reaction in step b) canadvantageously be removed by simple phase separation.

The organic diphosphites (II) are advantageous as ligands for catalystsfor hydroformylation, hydrocyanation or hydrogenation.

The invention will be illustrated below with the aid of the following,nonlimiting example.

EXAMPLES Example 1 Synthesis of6-chlorodibenzo[d,f][1,3,2]dioxaphosphepin using methylimidazoliumhydrochloride as catalyst

2,2′-Dihydroxybiphenyl (931.1 g, 5.0 mol) and1-methylimidazoliumhydrochloride (0.9 g, 7.6 mmol) were placed undernitrogen in a 2000 ml double-walled reactor and, after melting of the2,2′-dihydroxybiphenyl, heated to an internal temperature of 142° C. Theintroduction of PCl₃ (861.2 g, 6.263 mol) was then commenced withstirring, ensuring that the PCl₃ did not get onto the hot reactor wall.The rate of introduction was regulated so that the attached HClscrubbing tower could completely absorb the HCl formed. A total of threehours were required for the introduction of the PCl₃. After theintroduction of the PCl₃, the mixture was stirred at 140° C. for anotherthree hours to give a fluid yellow reaction mixture. The reactor wassubsequently evacuated over a period of 40 minutes to a final vacuum of16 mbar in order to remove the excess PCl₃. The last residues of PCl₃were removed by stirring under reduced pressure at 140° C./16 mbar andthe mixture was subsequently cooled to 65° C. After admission ofnitrogen, toluene (139.2 g) was added and the 90% strength solution(1390 g) of the product obtained in this way was drained into ascrew-cap bottle and closed under argon. According to ³¹P-NMR, theproduct had a purity of 98.7%.

The invention claimed is:
 1. A process for preparing6-chlorodibenzo[d,f][1,3,2]dioxaphosphepin (I)

which comprises reacting 2,2′-dihydroxybiphenyl (A1)

with PCl₃ in the presence of a catalytic amount of an acid salt of anitrogen base, wherein the reaction is carried out in the absence ofexternal organic solvents.
 2. The process of claim 1, wherein the acidsalt is derived from a nitrogen base selected from the group consistingof imidazoles, pyridines, 1H-pyrazoles, 4H-pyrazoles, 1-pyrazolines,3-pyrazolines, imidazolines, thiazoles, oxazoles, 1,2,4-triazoles, and1,2,3-triazoles, and wherein each member of the group is optionallyunsubstituted or substituted.
 3. The process of claim 1, wherein theacid salt is derived from an acid selected from the group consisting ofhydrogen chloride, p-toluenesulfonic acid, methanesulfonic acid,2,4,6-trimethylbenzoic acid, and trifluoromethanesulfonic acid.
 4. Theprocess of claim 1, wherein the acid salt of a nitrogen base isN-methyl-imidazolium hydrochloride.
 5. The process of claim 1, whereinthe amount of the acid salt of a nitrogen base used is from 0.01 to 5mol %, based on the molar amount of (A1).
 6. The process of claim 3,wherein the amount of the acid salt of a nitrogen base used is from 0.05to 2 mol %, based on the molar amount of (A1).
 7. The process of claim4, wherein the amount of the acid salt of a nitrogen base used is from0.1 to 1 mol %, based on the molar amount of (A1).
 8. The process ofclaim 1, wherein said process is carried out essentially withoutaddition of free nitrogen bases.
 9. The process of claim 1, wherein themolar ratio of the gradually added PCl₃ to the amount of (A1) used ismore than 1:1 at the end of the reaction.
 10. The process of claim 6,wherein the molar ratio of the gradually added PCl₃ to the amount of(A1) used is at least 1.1:1 at the end of the reaction.
 11. The processof claim 7, wherein the molar ratio of the gradually added PCl₃ to theamount of (A1) used is at least 1.2:1 at the end of the reaction. 12.The process of claim 1, wherein the molar ratio of the gradually addedPCl₃ to the amount of (A1) used is not more than 2.5:1 at the end of thereaction.
 13. The process of claim 1, wherein the molar ratio of thegradually added PCl₃ to the amount of (A1) used is not more than 2:1 atthe end of the reaction.
 14. The process of claim 10, wherein the molarratio of the gradually added PCl₃ to the amount of (A1) used is not morethan 1.8:1 at the end of the reaction.
 15. The process of claim 11,wherein the molar ratio of the gradually added PCl₃ to the amount of(A1) used is not more than 1.6:1 at the end of the reaction.
 16. Theprocess of claim 1, wherein the molar ratio of the gradually added PCl₃to the amount of (A1) used is not more than 1.4:1 at the end of thereaction.
 17. The process of claim 1, wherein (A1) is used as a melt forthe reaction.
 18. The process of claim 1, wherein a melt of (A1) isplaced in a reaction zone, and the PCl₃ is fed as feedstream into thereaction zone over the course of the reaction.
 19. The process of claim18, wherein the PCl₃ is introduced into the space above a melt of (A1).